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Transportation
Americans Learn to Do the Twist With European Drilling Technology
(enr.com-
8/27/01)
By >William J. Angelo and David B. Rosenbaum
European hydraulic drilling technology, used
for decades to install foundations in tight urban environments where
noise and vibration can adversely impact nearby structures, now
is seeing widespread use in the U.S. While costly, the machines
easily can core through tough obstructions to provide efficient
rock-socketed solutions and are quietly replacing mechanical rigs.
"The foundation industry was ripe for
a change," says Eric O'Neill, president of New England Foundation
Co. Inc., Quincy, Mass. "We used to keep equipment for decades
and all you had to do was change the moving parts. But then the
market moved towards drilled shafts because they are clean, simple
and direct. They can carry higher capacity loads, replace large
numbers of piles and are seismically desirable because of their
lateral load capacity. That required new equipment, which the Europeans
had already developed."
The new equipment includes crawler-mounted
drill rigs and crane-mounted rotators and oscillators that drive
steel casings into the ground to create and protect a hole. The
casing is withdrawn after the concrete shaft is poured. Gil Peel,
vice president of American Equipment & Fabricating Corp., East
Providence, R.I., estimates that there are about 300 rigs in use
in the U.S. "It took us from 1990 to 1995 to sell five rigs,"
he says. "Then in January 1996 we sold six, and since then
another 154."
Of the machines, crane-mounted rotators and
oscillators remain rarest. "There may be 10 oscillators and
perhaps two or three rotators in the U.S.," says Peel. According
to Peel, rigs can cost anywhere from $300,000 to $1-million, while
a 3-meter rotator will run about $1-million and a 1-meter oscillator
about $75,000 and 2-meter version $200,000. Notes Christian Gress,
sales director of Bauer Equipment, Natick, Mass.: "Mechanical
systems are being replaced by hydraulic systems because you can
use a small machine to produce tremendous force and handle multiple
functions simultaneously. It's like the history of excavators–nobody
uses cable operated buckets anymore."
The rigs now are now a mainstay item at industry
shows. Dallas-based ADSC: The International Association of Foundation
Drilling hosts equipment shows every three years. "In 1982,
Casagrande first showed one of their rigs but our guys were very
‘Buy American' and they didn't make much headway," says
Ted Ledgard, ADSC administrative director. He attributes the recent
economic boom for the European success. "U.S. manufacturers
were not quite ready for the boom and the Europeans had inventory
and were willing to lease," he explains. Ledgard also attributes
some of their success to the Texas Dept. of Transportation. "They
did some load tests on drilled shafts in the mid-1960's and found
them cheaper to install and that basically jump-started highway
use for drilled shafts," he says. "Now it's pretty much
the foundation of choice for most state DOTs and these rigs are
accepted as a basic foundation tool."
Even old-line firms are seeing the light.
"Mechanical crane rigs are our claim to fame," says Edmund
Cardoza, vice president of The Millgard Corp., Livonia, Mich. "But
we bought our first hydraulic rig last year and we're considering
buying more. They are great on tight sites and their torque and
down-pressure capacity has expanded so that now they can drive well
in excess of 150-ft deep." Before the hydraulics arrived, firms
used mechanical truck-mounted and crane-mounted rigs. "The
truck units were useful for small diameter shallow shafts, whereas
big projects needed a large crane with a big drill unit and sometimes
twin motors," he says. "We still use them, but more and
more projects have space constraints and that's where the European
units come in handy."
For the first time on a California highway
project, hydraulics are being used to drill bridge shafts near Truckee
as South San Francisco-based Malcolm Drilling Co. Inc. struggles
to core through 50 ft of glacial till and extraordinarily hard boulders
measuring several feet in diameter. Last year, crane-mounted mechanical
drilling sputtered nearby after AGRA Foundations Inc., Richmond,
Calif. tried to penetrate 20 ft of glacial till with boulders up
to 15 ft in diameter to construct foundations for an $8.5-million
bridge on S.R. 267 along the new Truckee Bypass. AGRA attempted
to rotate a 6.5-ft-dia steel core barrel, 2-in. thick and fitted
with teeth on the cutting end. "They weren't making the money
they need to make," says David F. Catania, a Caltrans transportation
engineer. With about half of the 54 piles drilled, the agency let
AGRA dig 50-ft-sq holes at each remaining footing. AGRA promptly
removed the boulders, installed the 4-ft-dia piles in half the time
as before, and completed the foundations on schedule.
Watching AGRA, Malcolm officials decided to
use a hydraulic rotator to construct 100-ft deep rock-socketed foundations
for three replacement bridges on Interstate 80. The foundations
in the $3.2-million contract are near water and regulators forbade
the use of glory holes. "When you get into the boulder patch,
we'll get the hole done better, faster and at less cost," insists
Ed Bucher, Malcolm area manager. "It's probably 50% faster."
That remains unproven. Just two of 21 piles have been completed
since June and Malcolm already is claiming differing site conditions,
a 14-ft-thick layer of 25,000-psi rock.
Malcolm is using a German-made Leffer RDM
3000 rotator with greater torque but less downward pressure and
fewer revolutions per minute than AGRA's faster yet less costly,
domestically made mechanical auger. Both methods work similarly,
with the rotator and auger each spinning a steel casing fitted with
teeth on the cutting end. Malcolm's rotator rests on its own outriggers
and tracks, with an adjacent crane that is used to resist some of
the torque as well as provide hydraulic power. The rotator measures
nearly 30 ft long and nearly 19 ft wide.
"I think AGRA's approach to our job was
the best approach, because we were able to churn out a whole lot
of rpm," says Catania. But Bucher expects fewer problems and
foresees a 25% to 35% cost savings from the $3.5 million worth of
equipment. By comparison, a crane with a drill attachment costs
about $1.5 million, Bucher notes. The higher cost of rotators "is
probably why nobody's used them," says Alan F. Dever, Caltrans
transportation engineer. "But it's gaining in popularity and
other contractors will be using that equipment."
Equipment breakdown has complicated Malcolm's
work and the firm needed to replace two motors. But the breakdown
rate seems about the same for rotators and crane-mounted augers,
Malcolm officials say. Crane-mounted drills still are a staple of
Malcolm's inventory, even though the company claims the largest
fleet of rotators and oscillators in the U.S. But rotators give
Malcolm greater flexibility. "This pushes us into the realm
of very, very difficult work," Bucher says.
European drilling equipment has been kicking
around New England for a decade. "We've only gotten in the
drilling business since the hydraulic rigs have been around,"
says Jeffrey F. Maxwell, vice president of Hub Foundation Co. Inc.,
Harvard, Mass. "We bought the first hydraulic rig in New England
in 1990 and now we own five."
Hub currently is working on a tight 10,000-sq-ft
site in Boston's Theater District, drilling 90-ft to 140-ft shafts
for a new 11-story multi-purpose tower linking several buildings
together. "We are drilling nine soldier piles to shore up an
alley and 17, 4-ft diameter shafts to support the building,"
says James C. Maxwell, Hub president. "It's a small site surrounded
by theaters, occupied classrooms and offices and the owner did not
want any noise or vibration."
Hub's solution is a Soilmec 825, made in Italy.
"We used that rig because it has the appropriate power in a
compact package," says James Maxwell. "It has to drill
the holes, screw in the casing and handle the reinforcing cage because
there is no room for a service crane." When drilling, it emits
78 decibels.
To enter the site, the rig was eased down
a 12-ft-wide, 100-ft-long alley, a feat made possible because the
treads retract to 10 ft. The $1-million, 100-ton machine has a four-piece
Kelly bar and a rotary table mounted on the front of the mast. The
table produces 170,000-ft pounds of torque and 300-tons of lift
capacity. Coupling the table with an oscillator jumps the torque
to 2-million ft pounds.
Hub is using 30-ft casings on the job. "The
surface is collapsing and is very unstable," says James Maxwell.
"But after 30 ft, we're into clay and till that seems stable
and we'll keep the shaft open with slurry." Work on the $600,000
contract started in mid-August and will end in October.
Hub used a smaller Soilmec 518 to drill six
4-ft-dia shafts 25-ft deep at a tight site in nearby Dedham under
a $100,000 contract. "The rock-socketed shafts support one
end of a bridge abutment and we had to drill through basketball-sized
shot rock until we hit hard granite," says Jeffrey Maxwell.
The firm drilled and poured one shaft every
two days. "We use an auger to drill a starter hole then put
in our steel casing. A twister locks into the casing and drives
it into the ground. We use a smaller auger to excavate the hole,
then set the rebar cage and tremie pipe and pour. We pull the casing
immediately after the pour," says Jeffrey Maxwell.
"Drilling is the wave of the future because
an engineer feels more confident with drilled shafts knowing the
load is transferred to rock. That said, we seem better able to apply
downward pressure with our hydraulic rigs versus a comparable crane-mounted
rig and with very little down time," says Jeffrey Maxwell.
"Hydraulic rigs are just faster and more efficient."
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